Comments by Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 19 February 2020

    Hi,

    If your battery is a 12V battery, your 2500mAh divided by 80mA calculation is correct. If you are not getting around 30 hours of operation, you could measure the actual current your device is drawing to determine if it is drawing more than specified or if your battery has less capacity than specified.

    - Jan

  • New D24V150Fx 15A step-down voltage regulator family — our highest-power regulators yet!

    New D24V150Fx 15A step-down voltage regulator family — our highest-power regulators yet!

    - 6 December 2019

    Hi, Magnus.

    Things like the available space, direction of airflow, and amount of airflow you need are going to be very specific to the overall system, so I do not expect to offer a regulator like this with a particular fan as a general stock product. Can you share more about your application and what kind of a fan setup would be good for you?

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 6 November 2019

    Hi, John.

    "Daisy chain" is a bad term to use in this context because it's at least ambiguous, if not outright incorrect for the setup you are describing. You can wire the batteries in series (which is what I would call daisy chaining if I had to), positive of one to negative of the other, to get 24V with 5Ah, or you can wire them in parallel, positive to positive and negative to negative, to get 12V with 10Ah. That should give you about 10% more run time than a single 9Ah battery.

    Wiring batteries in parallel makes me a bit nervous since you are initially shorting out two different voltages, but you should be ok if they are two of the same units and you charge or discharge them to the same voltage before connecting them together.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 24 October 2019

    Anonymous,

    I used eight "C" alkaline cells. Nowadays, though, I would probably just use eight NiMH AA cells since they're cheap, easy to get, and have decent capacity. The nominal voltage is a bit under 12V, so if I really needed that higher voltage, I might use ten cells.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 24 October 2019

    Brad,

    You're kind of all over the place with the units, mixing Ah and A, which is the main point of this blog post. However, for your case, most of that isn't that relevant, anyway, since you have a much more specific application, and the main challenge for you is how to charge batteries. In general, you can't just "plug in the solar panel between the batteries and the motor". Lithium-based batteries are especially touchy and dangerous, so I would stay away from them unless you have a product that is a complete solution--and then you wouldn't need to ask how to set that up.

    If this were my project and I were trying to do it cheaply/minimally, I would see if a 12V lead-acid battery would give the blinds enough juice. They might run a little slower, but probably it will be ok. Lead-acid batteries are a lot more forgiving, and a 12V battery could probably be topped off by just connecting two of your 8.4V solar panels in series and through a diode.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 23 August 2019

    Hi.

    It's difficult if you cannot do any math. You could try that pack you're talking about, and if it doesn't last long enough, get a higher capacity one. If it ends up lasting way longer than you need, you'll know next time that you could get a smaller one.

    - Jan

  • Servo control interface in detail

    Servo control interface in detail

    - 12 July 2019

    Since you seem interested in the details, the speed is not "12.5 μs"; rather, it's ``(12.5 μs)/(10 ms)``. To see how much the position changes from one time to anther, multiply speed by time: in 20 ms, the position will change by ``20 ms * (12.5 μs)/(10 ms) = 25μs``. Kind of like if you have a car that is going 65 MPH, and you check its position two hours after an initial check, it should be 130 miles farther. That you happen to check 2 hours apart doesn't make 65 MPH stop being a useful measure.

    Your seeing that some descriptions say D and others D/2 gives us good indication that the term is not particularly well defined, or that it gets used sloppily, so there's not much point in having a "correct" definition since you still need to determine what the source using it means. I think deadband of D should be the whole region of no response, which therefore means some target plus or minus D/2.

    Servos are usually not going to just have proportional control. You can take a look at our Jrk motor controllers if you want to look more into what might go into a servo:

    https://www.pololu.com/category/95/pololu-jrk-motor-controllers-with-feedback

    - Jan

  • Servo control interface in detail

    Servo control interface in detail

    - 9 July 2019

    Hello.

    I think you can gradually increase the pulse rate to the servo while moving it around, and if it behaves normally, it will probably be fine. Be ready to cut power if it tries to go past its physical limits (end stops).

    The Micro Maestro does its internal position update math every 10 ms independent of the pulse rate. That keeps the positions sent to the servos over time the same even if you change the pulse rate. You seem to be focusing on the servo side (and how it can only get an update once per period T); the point is that the servo controller only tells the servo what to do once per T, and the rest of the time, it's getting ready to tell the servo the right thing at the right time. Think of a clock with a second hand that ticks every second: it's updating the time it's telling you once per second, even though internally there could be gears and pendulums and other things moving between the times when the second hand is moving. The details of what it's doing internally to give you the correct updates are going to vary from clock to clock.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 2 July 2019

    Jim,

    Battery voltages always fluctuate as they discharge, so you definitely don't need "the exact same numbers". Also, an AC power adapter does not have to connect to exactly the same point in the circuit as the batteries, so you shouldn't put too much stock in the power adapter specs for the purposes of battery selection. But in this case, the numbers match up since four AA alkaline batteries in series will give you 6V.

    I don't know what you mean by "they worked once" and what the relevance of that is. Does it mean that they don't work anymore, even after charging? In any case, alkaline batteries have a little higher voltage than NiMH batteries, 1.5V nominal vs 1.2V nominal, so four of those in series gets you to 6.0V vs. 4.8 V, so some devices don't work very well or very long if they really need the higher voltage. A charged NiMH cell might actually get to about 1.4V, so it looks a little like a somewhat discharged alkaline right off the bat.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 28 June 2019

    Hi, Jimmy.

    I think that depends too much on the details of the particular batteries and what exactly they've been through. Age-wise, those 4 months don't seem like too much of a difference, and 65 cycles also doesn't seem like that much, so my guess is you'll get more life out of the 2.0 Ah battery.

    - Jan

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